Abstract
In this study, energy and exergy analyses have been investigated numerically for unsteady cross-flow over heated circular cylinders. Numerous simulations were conducted varying the number of inline tubes, inlet velocity, dimensionless pitch ratios and Reynolds number. Heat leakage into the domain is modeled as a source term. Numerical results compare favorably to published data in terms of Nusselt number and pressure drop. It was found that the energy efficiency varies between 72% and 98% for all cases, and viscous dissipation has a very low effect on the energy efficiency for low Reynolds number cases. The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency. The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers. The results could be useful in designing more efficient heat recovery systems, especially for low temperature applications.
Highlights
External forced convection around circular cylinders has a great number of applications in heat exchangers, for space heating, power generators, condensers, electrical equipment and many other thermal applications
The exergy efficiency ranges from 40–64%, and the entropy generation due to heat transfer was found to have a significant effect on exergy efficiency
The results suggest that exergy efficiency can be maximized by choosing specific pitch ratios for various Reynolds numbers
Summary
External forced convection around circular cylinders has a great number of applications in heat exchangers, for space heating, power generators, condensers, electrical equipment and many other thermal applications. The authors obtained a dimensionless entropy generation rate for each geometry, which depended on Reynolds number, perimeter, the axis ratio for the elliptical pin fin and the aspect ratio They reported that the worst performance was found for the square geometry from the point of view of total heat transfer rate, drag force and entropy generation rate. The authors obtained a heat transfer coefficient parameter and suggested a Nusselt number correlation that depended on the longitudinal pitch, transverse pitch, Reynolds and Prandtl number They claimed that this model was applicable for a wide range of parameters over a bundle of tube banks in staggered or in-line arrangements. The purpose here is to determine optimal first and second law efficiencies for low-temperature heat recovery using banks of cylindrical tubes, especially for low temperature heat recovery
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